The present invention relates to seals, and more particularly to an improved seal for use in fluid dynamic systems.
Efficient operation of pressurized fluid systems, e.g., turbines, compressors and pumps, requires that high and low pressure operations be separate from one another. This is particularly true at the junctures of stationary and moving parts.
Many sealing systems have been developed for this purpose. Labyrinth seals, for example, use a segmented seal ring between a rotating part, e.g., a shaft, and a stationary part, e.g., a turbine casing. The seal ring has a plurality of seal teeth for reducing the radial gap between the shaft and casing to several thousandths of an inch. The seal teeth commonly extend radially inward and are spaced axially at intervals along the seal ring. The teeth are disposed in opposition to alternating raised portions on the shaft circumference. This arrangement forms a tortuous pathway for fluid flow which effects a seal between the shaft and the casing, separating high and low pressure regions along the rotating shaft.
However, during system start-up or shut-down when thermal distortion, shaft bowing, and vibration are most common, the teeth and the shaft often contact one another causing wear and damage to the seal.
In an attempt to solve this problem, a segmented ring is used with S-shaped springs between ends of adjacent seal ring segments. The springs bias the segments radially outward during minimum load conditions, e.g, system start-up or shut-down, in an attempt to increase the teeth to shaft clearance, while decreasing the clearance at the maximum load conditions encountered during normal operations. A seal of this general configuration is shown, for example, in U.S. Pat. No. 4,436,311, issued to Brandon on Mar. 13, 1984, the disclosure of which is hereby incorporated by reference.
However, each seal ring segment is constrained by only one set of springs whereby failure of one spring results in loosening of the seal segment and, hence, failure of the entire seal ring during normal operations. Moreover, these segments are known to lock in an open position during minimum pressure operations.